Abstract
AbstractPoly(N‐isopropylacrylamide) (PIPA) was synthesized by radical polymerization with 2,2′‐azobisisobutyronitrile (AIBN) as an initiator and 3‐mercaptopropionic acid (MPA) as a chain‐transfer reagent in methanol (MeOH) at 70°C for 7 h. The resultant PIPA was grafted to polyallylamine hydrochloride (PAIAm · HCI) by amide formation under the influence of water‐soluble carbodiimide 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide hydrochloride (EDC). The graft polymer was made into microspheres (MS) by chemical crosslinking. The pH‐responsive drug release of the graft polymer microspheres was examined by releasing phenobarbital natrium (PN), which was carried on the microspheres by physical adsorption. A dynamic dialysis technique was used in the drug‐release experiment and the drug‐release‐rate constants reflecting the drug release characteristic of polymer microspheres were obtained by constituting a mathematical model. The results indicated that the homopolymer PAIAm microspheres and the copolymer PAIAm‐g‐PIPA microspheres are both pH responsive to release PN and that in the neutral pH condition the release rate is the slowest. © 1995 John Wiley & Sons, Inc.
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